Fusible protective device



Dec 27, 1966 M. G. LEONARD ETAL 3,294,935

FUSIBLE ROTECTIVE DEVICE Filed Dec. 26, 1961 5 Sheets-Sheet 1 ATTORNEYDec. 27, 1966 M. G. LEONARD ETAL 3,294,935

FUSIBLE PROTECTIVE DEVICE Filed DeC. 26, 1961 Fig. IO.

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FUSIBLE PROTECTIVE DEVICE Filed Deo. 26, 1961 3 Sheets-Sheet 5 Fi ll.48h g 48 500 nooo 50o IOO IN SECONDS TIME l lllllll 0, ||1lm |r||m| 15o50o |ooo zooo |oooo CURRENT |N AMPEREs United States Patent C 3,294,935FUSIBLE PROTECTIVE DEVICE Merrill G. Leonard, Brookfield Township,Trumbull County, Ohio, and John J. Astleford, Jr., Sharon, Pa.,assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., acorporation of Pennsylvania Filed Dec. 26, 1961, Ser. No. 162,144Claims. (Cl. 200-120) T-his invention relates to fusible protectivedevices in general, and, fmoreiiparticularly, t-o fusible protectivedevices of the type utilizing a plurality of fuse links in series forclearing the associated circuit.

A general obje-ct of the present invention is the provision of animproved fusible protective device particularly suitable for theefficient -clearing of the associated circuit and of economicalconstruction for mass lproduction.

A more specific object of the present invention is the provision of lanimproved two-break fusible assembly particularly adaptable forinterrupting a wide range of currents.

A further object of the present invention is to provide an improvedprotective device of the fusible type suitable for immersion in .anarc-extinguishing liquid, such as oil, and highly efficient inoperation.

Yet a further object of the present invention is the provision of asuitable fusible protective device applicable to oil-immerseddistribution transformers, such, for example, as those having a 167 kva.rating, which will clear high-value fault currents, such, for example,as 10,000 amperes at 12,000 volts.

Still a further object of the present invention is the provision of atwo-break fuse assembly of the oil-immersed type, in which two breaks inseries are established, with one break forcing oil to flow underpressure toward the other series break for a short clearing time.

Yet a further object of the present invention is the provision of animproved fusible assembly involving few parts and adapted forfacilitated fabrication.

An ancillary object of the present invention is the provision of animproved fusible protective device having biasing means, such, forexample, .as spring means associated 4therewith for the rapidinterruption of low-value currents, and having two series fusibleelements for establlishing two fusible breaks in t-he circuit, wherebyone of the fusible breaks preferably forces uid to ow toward the otherfusible break for rapid interruption.

Although certain features of the present invention are particularlyadaptable for distribution transformer use, involving oil as thearc-extinguishing liquid,` nevertheless, it will be apparent to thoseskilled in the art, that certain features of the present invention areapplicable to other arc-extinguishing mediums than oil; and,accordingly, the improved fuse structure of the present invention may beapplied, when desired, to gas-filled enclosures, or even utilized in anair ambient at atmospheric pressure.

Further objects and advantages will readily become apparent upon readingthe following specifi-cation, taken in conjunction with the drawings, inwhich:

FIGURE 1 is a fragmentary vertical sectional view, partially in sideelevation, .and partially diagrammatic, of the improved fusibleprotective device of the present invention utilized in a subwaydistribution transformer tank-assembly of the oil-filled type;

FIG. 2 is an enlarged fragmentary side elevational view of theconnection between the fusible device of the present invention and theinterior projecting stud end of the pothead assembly for the tankstructure of FIG. l;

FIG. 3 is a vertical longitudinal sectional view taken through thefusible 'assembly of the present invention with the series fuse elementsshown in their intact condition;

3,294,935 Patented Dec. 27, 1966 ICC FIG. 4 is a top plan view of thefusible protective device of FIG. 3;

FIG. 5 is a detailed end elevational view of the insulating orifice plugutilized in the fuse casing assembly;

FIG. 6 is a side elevational view of the insulating orifice plug of FIG.5;

FIG. 7 is an enlarged detail side elevational view of the two-breakfusible assembly of FIG. 3 illustrated in its intact condition;

FIGS. 7A and 7B illustrate cross-sectional views taken through amodified-type two-break fuse assembly, wherein one fuse element islarger than the other fuse element;

FIGS. 8 and 9 are sectional views taken respectively along the linesVIII-VIII and IX-IX of the fuse assembly of FIG. 7;

FIG. l0 is a view similar to that of FIG. 3, but illustratin-g thecondition of the several parts upon fuse rupture;

FIG. 11 illustrates, in vertical cross-section, a modifiedtype two-breakfusible protective device, the fuse elements being illustrated in theirintact condition;

FIG. l2 is a vertical sectional view, similar to that of FIG. 1l, butillustrating the disposition of the several parts upon fuse rupture;and,

FIG. 13 is a graph showing clearing time as a function of current forthe device of FIG. 3.

Referring to the drawings, and more particul-arly to FIG. 1 thereof, thereference numeral 1 generally designates a subway distributiontransformer tank-assembly having an interiorly-disposed transformer 2associated therewith. As shown, the transformer 2 is submerged intransformer oil 3, and 4has a pothead assembly 4 associated therewith.

Fixedly secured to the lower interior end 5 of the pothead assembly 4 isthe protective device 7 of the present invention partially enclosed byan insulating support tube 10. It will be noted that the electrode S ofa fuse assembly 9 (FIG. 3) `is threadedly secured to the interior end 11of the stud-assembly associated with the pothead 4. FIG. 2 illustratesmore clearly the associated threaded relationship of the stud 11 withthe electrode 8.

With reference to FIG. 3 of the drawings, it will be observed that thereis provided an insulating casing 12 of generally tubular construction.The casing 12 preferably has three shoulder portions 13-15 formed alongthe inner wall thereof. Additionally, the insulating fuse casing 12 ispreferably formed of a suitable gas-evolving material, such as fiber, orthe like.

The electrode 8 of the fuse assembly 9, as shown, has a 4pair ofaxially-aligned threaded recesses 16, 17. The threaded recess 16 isadapted for threaded connection to the stud 11, as previously mentioned.The threaded recess 17 is adapted to threadedly receive a stlud 18 (FIG.7) associated with a two-break fusible device, generally designated bythe reference numeral 9, and shown more in detail in FIGS. 7-9 of thedrawings.

With reference to FIG. 7, it will be noted that the stud 18 has aconnecting portion 18a, to which is secured, as by brazing, an inner, orfirst fusible element 22, of round, wire-like configuration, as shown inthe sectional view of FIG. 8. Although shown as round wire-likeconfiguration, the fusible element 22 could have other cross-sectionalconguration, such as square, or rectangular, as desired.

To the lower end of the fusible element 22, as viewed in FIG. 7, issecured, as by brazing, a substantially U-shaped connector 23:preferably of strap-like configuration. As shown in FIG. 7, theconnector 23 preferably has ixedly secured thereto, as by brazing, astop element 24. Preferably, the connector element 23 and the stopelement 24 are formed of a suitable metallic material, such, forexample, as copper strap. For one particular application, the connector23 may be formed of 313/52 x 3/8" :of .063H thick copper strap. The stopelement 24 may be formed of similar strap material.

Fixedly secured, as by brazing, to the lower end of the connectorelement 23, as viewed in FIG. 7, is :an outer, or second fusible element27, having a configuration and size similar to that of thefirst-mentioned fusible element 22. For example, the fusible elements 22and 27 may be formed, for example, of .064" round fusible wire. T-oobtain selective melting, the first fuse link 22 is shorter in length lthan the second fuse link 27, the length of which is indicated by L, asshown in FIG. 7. For a particular example, the length l may be 3/8whereas the length L may be Ss. As a result, for -relatively lowv-aluefusing currents, the element 27 may be the only one to melt, whereas onlarger fusing currents both elements 22, 27 will fuse substantiallysimultaneously creating two breaks in the circuit.

Fixedly secured to the lower end of the outer, or second fusible element27 is a fuse ferrule 28, the lower end of which, in turn, is fixedlysecured to a conducting cable 30.

As shown in FIG. 3, the flexible conducting cable 36 has a cup-washer 31threaded thereon tand secured thereto by a crimping connection 32.Interposed between the cupwasher 31 and the shoulder portion 15 `of thetubular casing 12 is a biasing compression spring 34, which serves thepurpose of maintaining the fusible :assembly 9 and the fusible elements22, 27 thereof in tension.

During a heavy fault-current condition upon the line to be protected, asmentioned, the two fusible elements 22, 27 of the fusible assembly 9will rupture, forming thereby two breaks in series, as illustrated inFIG. l of the drawings. It will be noted that a first, orpressuregenerating break 35 is formed between the remaining ends of thefirst fusible element 22, whereas a second, or interrupting break 36 isformed lbetween the ends of the outer, or second interrupting fusibleelement 27. A blast of fluid is ejected under pressure from the firstbreak 35 toward the second break 36, as indicated by the arrows 20 inFIG. 10. Where, in the particular application, oil 3 is 'theinterrupting medium, it will be obvious that a blast of un-ionized oilparticles will be ejected tow-ard the sec- -ond break 36. In addition,the iaction of the biasing compression spring 34 will be effective toaccelerate the opening separating movement of the second, orinterrupting break 36.

For certain applications it may be desirable to have the cross-sectionalarea of the inner, or first fusible element 22 somewhat larger than thecross-sectional area of the second fusible element 27. This state ofaffairs is illustrated in FIGS. 7A and 7B of the drawings, whichrespectively `are cross-sectional views taken through a modifiedtype offusible assembly 9a, wherein the respective crosssectional areas of thefuse elements 22a, 27a have the aforementioned relative dimensions. As aIresult of such a modified construction, the second fusible element 27awould tend to rupture first at relatively low currents, and possiblymight be the only fusible element of the assembly 9a to rupture. Forhigher-value currents, both elements 22a, 27a would rupture; and theinterrupting action would take place as in the first-mentionedembodiment 9 of FIG. 3 of the drawings.

FIGS. 1l and 12 illustrate a fusible modification 49 of the inventionwherein a fuse casing 50 has a bore extending therethrough and threadedend portions 50a, 50h. Threaded into the upper end of the fuse casing 50is a terminal plug 48, which closes this end of the casing 50. Aconnector strap 48a may be `afiixed by a terminal bolt 48]; to the upperterminal 4S to serve as a connection to the circuit to be protected.

Threaded into the lower end Sfib of the tubular fuse casing f) is anorifice plug 51 having an `aperture 52 therethrough. It will be notedthat a pellet 53 is attached to the fuse cable 54, so that the pellet 53may be subjected to the gas pressure and ejected out of the casing 50during the interrupting operation. In effect, therefore, apressuregenerating chamber 60 is provided interiorly of the fuse tubeSti, and pressure generated therein during fuse rupture. Preferably, thetop fusible element 70 is of a slightly larger cross-sectional area thanthe lower fusible element 71 so that at relatively low-value fusingc-urrents the lower fusible element 71 will be the 'only one to rupture.For higher fusing current levels, both fusible elements will rupture,thereby causing a blast of fluid, such as foil, from the upper, or innerarc to be ejected toward the second, or outer arc 81, Ias illustratedmore clearly in FIG. 12 of the drawings.

Preferably, the tubular fuse casings 12, 50 lof the various embodimentsare formed of `a gas-evolving material, such as fiber or the like. Inaddition, the apertured orifice plugs 6, 51 are likewise formed ofgas-evolving material, such `as ber for more efficienttare-extinguishing action.

From the foregoing, it will be apparent that the present inventionrelates to a new type of protective link 7, 49 for more powerfularc-extinguishing action, particularly when the protective link isdisposed in an oil ambient. It is believed that a basic new feature ofthe invention, as illustrated in FIGS. 11 and l2, is a three-sectionwire, the top section 70 being slightly larger than the bottom section71, and the central section 75 being much larger than either of theaforesaid sections 70, 71. For certain applications, as illustrated inFIGS. ll and 12, `an ejectable pellet 53 is a free fit within theapertured fiber orifice 51.

In the operation of the modified form of the invention illustrated inFIGS. ll and 12, the interrupting operation during low-value currentscauses the lower section 71 to blow first, thereby drawing an arc 81inside of the fuse orifice 51. For minimum fusing current, this sufficesto clear the circuit. For higher current levels, the upper, or innersection 70 blows an instant after the lower section 71. This causes anarc 80 at the inner section, which during expansion drives oil 3 aroundthe outer, or lower fusible element 71 and out through the fuse orificeopening 52. The result is a double-gap construction to quench the arc,plus forced oil fiow through one of these gaps. The forcible ejection ofthe pellet 53, attached to the fuse cable S4, further aids in arcextinction.

It is to be noted in the construction of FIGS. 1l and 12, that theintermediate fuse section 75 is not only much larger in cross-sectionalarea than the rst and second fuse elements 7i), 71, but preferably isflat or ribbonshaped in configuration so that it will not clog theorifice tube 51. It is believed that novelty resides, in part,concerning the combination in a fuse of a double-break, forced fluidfiow, such as oil fiow, through the are 81 in the orifice 52, and freetravel of a bottom electrode 53 through an arc-extinguishing medium,such as oil 3, below the fuse structure 49.

Remarkable interrupting results have been achieved with the fusestructure 7 illustrated in FIGS. 3-9 of the drawings. Successfulinterruption tests at l2 kv. were made on a 10,000-ampere protectivelink.

FIG. 13 illustrates, in graphical form, the aforesaid interruptingtests. It will be apparent that the time, as a function of current to beinterrupted, can be carefully controlled to the desired time values.

Although certain features of the present invention have particularapplication when utilized in connection with a suitablearc-extinguishing liquid, such as oil, nevertheless it will be apparentto those -skilled in the art that other suitable arc-extinguishingmediums, such as sulfur-hexafiuoride (SP6) gas, selenium-hexafluoride(SeF) gas, sulfur, etc., or even air at atmospheric pressure may beemployed.

Although there have been illustrated and described certain specific fusestructures, it is to be clearly understood that the same were merely forpurpose of illustration, and that changes and modifications may readilybe made by those lskilled in the art, without departing from the spiritand scope of the invention.

We claim as our invention:

1. A fusible device including a tubular casing having an electrodeassembly blocking one end thereof, the other end of said tubular casingbeing open, a unitary two-break fuse assembly disposed within the casingand including a pair of spaced fusible elements, an orifice plug fixedlyse* cured against said open end of the casing, biasing means fortensioning both the pair of fusible elements of the fuse assembly, andconducting spacing means associated with the two serially-related fuseelements having stop means associated therewith to limit the length ofone of the arcs.

2. The fusible device of claim 1, wherein one of the fusible elementshas a smaller cross-sectional area than the other.

3. The fusible device of claim 1, wherein one of the fusible elements ispositioned adjacent the orice plug and is suitable dimensioned to fusebefore the other serially-related fusible element during low-valuefusing currents.

4. The combination of claim 1, wherein the conducting spacing means issubstantially U-shaped so as not to block the open end of the casing.

5. The fusible device of claim 1, wherein a fuse cable is secured to thefuse assembly and extends out the open end of the casing.

6. The combination according to claim 5, wherein the biasing meanscomprises a compression spring seated on a spring seat secured to thefuse cable.

7. The combination according to claim 1, wherein one of the fusibleelements is of greater length than the other.

8. A fusible device including a generally tubularlyshaped casing atleast partially of insulating material, means closing one end of saidcasing, the other end of said casing being at least partially open,terminal means disposed adjacent said one end of the casing, unitarydouble-break fusible means positioned at least partially within saidcasing and having one end thereof electrically connected to saidterminal means, said fusible means including a pair of spaced fusibleelements, biasing means associated with said other end of the casing andtensioning .said unitary double-break fusible means las a unit to anopen-circuit condition, and stop means associated with said spacedfusible elements to limit the length of one of the established arcs.

9. In combination, a fusible device adapted for the protection oftransformers, or the like, including a tubular casing, electrode meansclosing one end of the casing, the other end of the casing being open,tensioning means situated adjacent said other end of the casing, aunitary two-break fuse assembly disposed within the casing and includinga pair of spaced fusible elements and an inter- 6 vening conductingspacing means, said tensioning means acting to tension both elements ofsaid double-element fuse assembly, and stop means associated with theintervening conducting spacing means to limit the length of one of thearcs.

10. The fusible device of claim 9, wherein one of the pair of spacedfusible elements is disposed adjacent the open end of the casing and isso dimensioned so as to fuse before the other serially-related fusibleelement during low-value fusing currents.

11. The fusible device according to claim 8, wherein one of the spacedfusible elements is situated adjacent the open end of the casing, andsaid one fusible element is s0 dimensioned so as to fuse before theother serially related fusible element during low-value fusing currents.

12. A fusible device including a generally tubularlyshaped casing atleast partially of insulating material, means closing one end of saidcasing, the other end of said casing being at least partially open,terminal means disposed adjacent said one end of the casing, unitarydouble-break fusible means positioned at least partially within saidcasing and having one end thereof electrically connected to saidterminal means, said fusible means including a pair of spaced fusibleelements, and stop means associated with the spacing means for said`pair of spaced fusible elements to limit the length of one of theestablished arcs.

13. The combination according to claim 12, wherein a pellet (53)attached to the fusible means is disposed within the open end of thecasing so as to be subjected to gas pressure and thereby assist thefusing operation.

14. The combination according to claim 12, wherein one fusible elementis so dimensioned as to fuse before the other serially-related fusibleelement during low-value fusing currents.

15. The combination according to claim 12, wherein one of the fusibleelements is positioned adjacent the open end of the casing and is ofgreater length than the other fusible element.

References Cited by the Examiner UNITED STATES PATENTS 2,050,277 8/1936Crabbs et al. 200-117 2,090,609 8/1937 Lemmon 200*l35 2,094,012 9/1937Hill 20G-l2() 2,162,540 6/1939 Triplett 200 l35 2,180,975 ll/1939 Brown200- 2,199,746 5/1940 Hart 200-135 2,208,440 7/1940 Williams 20D-1272,245,188 6/1941 Earle 200-117 2,896,050 7/l959 Tomlinson 200-1 172,959,652 ll/l960 Gaslill et al 20G-127 BERNARD A. GILHEANY, PrimaryExaminer.

1. A FUSIBLE DEVICE INCLUDING A TUBULAR CASING HAVING AN ELECTRODEASSEMBLY BLOCKING ONE END THEREOF, THE OTHER END OF SAID TUBULAR CASINGBEING OPEN, A UNITARY TWO-BREAK FUSE ASSEMBLY DISPOSED WITHIN THE CASINGAND INCLUDING A PAIR OF SPACED FUSIBLE ELEMENTS, AN ORIFICE PLUG FIXEDLYSECURED AGAINST SAID OPEN END OF THE CASING, BIASING MEANS FORTENSIONING BOTH THE PAIR OF FUSIBLE ELEMENTS OF THE FUSE ASSEMBLY, ANDCONDUCTING SPACING MEANS ASSOCIATED WITH THE TWO SERIALLY-RELATED FUSEELEMENTS HAVING STOP MEANS ASSOCIATED THEREWITH TO LIMIT THE LENGTH OFONE OF THE ARCS.